Our Montney clients often ask us: “What is the optimal/ideal for frac optimization?” Of course, this is a million-dollar question!
Montney is a very large play. The targeted play can reach up to 300-400 meters in thickness. Multiple subunits exist within the Montney play. Some subunits have been extensively developed and some remain still undeveloped. Many operators have started to tap on less developed areas and in some instances, results have been outstanding.
Montney wells usually require a large hydraulic frac job to fully realize their potential. The behaviour of frac growth and subsequent frac interactions in complex well configuration schemes combined with subtle geological and geomechanical environments is not fully understood. Fortunately, many Montney operators have started to adopt new surveillance techniques, such as micro-seismic mapping, downhole pressure monitoring systems, and stage-by-stage flow-backs in combination with fiber optics to better understand the frac behaviour.
One of the key drivers of frac behaviour which hasn’t received enough attention is the impact of geomechanics of the landing interval on the frac propagation. Montney usually exhibits substantial mechanical heterogeneity within all its subunits including the Upper, the Middle and the Lower Montney. Targeting the geomechanics sweet spots appears to be an important driver for frac optimization.
A few key questions to consider:
(1) How the geomechanics of the landing interval impacts the dynamics of out-of-zone frac growth, as well as the size of the stimulated rock volume and propped zones.
(2) How the geomechanics of the landing interval impacts the cluster efficiency and the conformity of the frac half length and frac height growth in multi-cluster plug and perf frac jobs.
There is extensive discussion in the unconventional rocks community about the best proxy to rank and evaluate the rock competency for frac optimization. Geologists have adopted traditional methods (widely used in porous and permeable conventional rocks) for unconventional tight rocks based on the geological characteristics, such as porosity, clay content, saturation, Total Carbon Content (TOC). Geomechanics use different approaches, such as Brittle Index (BI) or modified BI constructed from geomechanics logs and triaxial tests. Geophysicists use the mud rock line or Lambda-Mu-Rho (LMR) approach. Recently, some influencers have proposed using the minimum in-situ stress as the primary driver for hydraulic fracturing optimization. This begs the questions:
- Which proxy is the best to use?
- Can we define a universal approach to identify the optimal landing intervals acknowledging all disciplines including geology, geomechanics and geophysics?
In this blog, I will provide insights on how to use a new universal Mechanical Competency Index (MCI) to identity the geomechanical sweet spots. This will characterize fracability and how to optimize well placement with the Montney formation as a test case. In my earlier GLJ Insights Blog titled “New insights into shale fracability in Kaybob Duvernay,” we discussed this criteria and demonstrated the importance of the landing intervals.
Let’s look at the Montney formation as an example. Figure 1 illustrates the constructed MCI versus True Vertical Depth (TDV) for a three well pad in the liquid rich part of the Montney in British Columbia. Rocks are geomechanically more competent when this index is closer to zero.
Two wells are completed in the upper Montney (liquid rich) and one well in the middle Montney (leaner gas). The MCI is constructed by incorporating a broad range of available data including Diagnostic Fracture Injection Test measurements, dipole sonic and rock mechanics characterization.
As expected, non-reservoir formations such as Doig, Doig Phosphate, and Belloy are all geomechanically incompetent, creating potentially effective containment intervals for fractures completed in the Montney play. This is shown in the figure below in the dark blue colour in the colour bar. It is important to note that every rock can potentially break under the extensive forces generated by hydraulic fracturing. This is dependent on many factors including the proximity of the well to containment zones and size of the frac job, the frac pumping rate and the treatment pressure.